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XXIII. Influence of Gravity on Magnetic Declination. 

 By Pliny Earle Chase, M.A., S.P.A.S.* 



JN my first communication on the diurnal variation of the 

 barometer (Proceedings Amer. Phil. Soc. vol. ix. p. 284), I 

 expressed the belief that a careful investigation would " show a 

 mutual connexion through which all the secondary [disturbing] 

 causes may be referred to a single force." In my various sub- 

 sequent papers, and especially in the one to which the Magel- 

 lanic Premium was awarded (Phil. Mag. July 1865), I pointed 

 out various reasons for supposing that the primal unitary force 

 is the same that controls the motions of the several stellar sys- 

 tems — in other words, the force of gravitation, or perhaps of 

 simple undulation, which is manifested as heat in one of its sub- 

 ordinate forms, and as attraction in another. The numerical rela- 

 tions which I demonstrated between the disturbances of weight 

 and of total magnetic force were certainly noteworthy, and, to 

 my own mind, extremely satisfactory ; and as further investi- 

 gations have afforded additional confirmation of my views, I 

 desire to put upon record a brief notice of the general har- 

 mony which mutually characterizes the gravitation-currents and 

 the variations of magnetic declination. 



Preliminary investigations showed, as might have been rea- 

 sonably anticipated, that the best quantitative results can be 

 obtained from the observations at stations near the equator, and 

 I therefore based my reasoning in great measure upon the St. 

 Helena records and Major General Sabine's discussions, confirm- 

 ing it by such incidental references to other observations as 

 seemed available for the purpose. At the same time allusion was 

 made to researches now in progress, which may probably enable 

 us to discover numerical relations that will be equally satisfac- 

 tory from an examination of the observations in higher latitudes. 

 While patiently and confidently awaiting the completion of those 

 researches, it may be well to present some considerations which 

 will serve both as a corroboration of my own views and as a 

 guide to the investigations of others. 



The discussions of the magnetic and meteorological observa- 

 tions at Girard College (Coast Survey Reports, and Smithsonian 

 Contributions) should be specially interesting to all Americans, 

 and they are also among the most recent and valuable publica- 

 tions on terrestrial physics. Prom them I quote the following 

 references to the most important and best-established normal 

 disturbances of declination. 



I. " The annual variation depends on the earth's position in 



* From Silliman's American Journal for July 1865. 



